1. Field of the Invention
The present invention relates to a process for the obtaining, with high yields and for the recovery in high proportion, of glyoxylic acid hemiacetal-esters.
2. Description of the Prior Art
Glyoxylic acid hemiacetal-esters are principally used at present for preparing the corresponding esters by the action of P.sub.2 O.sub.5 (W. OROSHNIK and P. E. SPOERRI, "J. Amer. Chem. Soc." 1941, 63, 3338) and this method is only used for preparing the esters of lower alcohols. The esters of alcohols with C.sub.4 and more and notably butyl glyoxylate are currently obtained by the oxidation of the corresponding tartaric esters by lead tetraacetate (Organic Syntheses, coll. vol. IV p. 124) or by periodic acid (T. R. KELLY, Th. E. SCHMIDT and J. G. HAGGERTY Synthesis, 1972, (10) 544-5). The esters of arylaliphatic alcohols can be prepared by the action of an alkali or alkaline-earth glyoxylate on an aralkyl halide (German Patent Application No. 2,403,445). In fact, it is not possible to obtain aldo-esters by direct esterification of glyoxylic acid by alcohols, although, in contradiction with all known teachings, certain authors (German patent application No. 2,241,862) describe the preparation of glyoxylic esters of C.sub.4 -C.sub.10 alcohols by condensation of glyoxylic acid with the alcohol in the presence of a strong acid catalyst.
It is known that when glyoxylic acid is reacted with an alcohol in the absence of a catalyst, the glyoxylic hemiacetal-ester is essentially obtained containing a little glyoxylic ester and glyoxylic-acetal-ester, whereas in the presence of a strong acid as catalyst it is rather the acetal-ester which is formed (German Pat. Nos. 928,405 and 1,004,158). The condensation of glyoxylic acid in aqueous solution with alcohols, in the absence of a catalyst and with the elimination of water, either by prior concentration of the aqueous glyoxylic acid solution, or in the course of the reaction by azeotropic dehydration, has been in fact proposed for manufacturing glyoxylic hemiacetal-esters (German Pat. No. 1,004,158). However this process gives relatively low yields of hemiacetal-ester for alcohols of C.sub.4 and more.
Accordingly it is an object of the invention to provide a process for increasing the yields of glyoxylic acid hemiacetal-esters.
It is a further object of the invention to provide an improved process for producing glyoxylic acid hemiacetal-esters of alcohols of C.sub.4 and more.
It is another object of the invention to provide a process for recovering glyoxylic acid hemiacetal-esters in high proportion from media containing them.
It is another object of the invention to provide a process for producing glyoxylic acid esters in improved yields.
Other objects and advantages of the invention will be apparent from the description which follows.
Applicant has found that if the hemiacetal-esters ##STR1## are subjected to heating under substantially anhydrous conditions, either in the course of their process of production after reaction of the glyoxylic acid OHC--COOH with a ROH alcohol, or in the course of the manufacture of aldo-esters OHC--COOR by the action of P.sub.2 O.sub.5 on the hemiacetal-esters, there is formed, especially where hemiacetal-esters of alcohols of C.sub.4 and more are concerned, a "bridged ketal" ##STR2## by dehydration between two hemiacetal-esters and that if, after having separated the remaining hemiacetal-esters, the resulting reaction medium is subjected to the action of a 85% phosphoric acid (H.sub.3 PO.sub.4) solution, an additional amount of hemiacetal-esters is obtained.
The production of the latter can be explained by the hydrolysis of the "bridged ketal" and/or of the acetal-esters possibly present in the medium.
This discovery has been applied in the present invention and can be utilised both in the manufacture of glyoxylic hemiacetal-esters by the action of glyoxylic acid on alcohols and in the utilization of hemiacetal-esters for the manufacture of esters by the action of P.sub.2 O.sub.5 on the hemiacetal-esters. Thus, therefore, in the first case the invention enables the yield of hemiacetal-esters to be considerably increased and in a second case the invention enables the recovery of the greater part of the hemiacetal-ester which has been dehydrated and not converted to aldo-ester.